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Reward enhances backward inhibition in taskswitchingHao Jianga & Baihua Xua

a Department of Psychology and Behavioural Sciences, Zhejiang University,Hangzhou, Zhejiang Province, ChinaPublished online: 24 Jan 2014.

To cite this article: Hao Jiang & Baihua Xu (2014) Reward enhances backward inhibition in task switching, Journal ofCognitive Psychology, 26:2, 178-186, DOI: 10.1080/20445911.2013.878717

To link to this article: http://dx.doi.org/10.1080/20445911.2013.878717

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Reward enhances backward inhibition in task switching

Hao Jiang and Baihua Xu

Department of Psychology and Behavioural Sciences, Zhejiang University, Hangzhou,Zhejiang Province, China

Recently, effects of reward incentives on interference-induced cognitive adjustments have drawn muchattention. It has been demonstrated that reward can reduce or eliminate switch costs which occurredwhen alternating between different tasks. However, it still remains a question how reward affectsinhibitory processes underlying task switching. The present study examined this issue by combining atask-switching paradigm with performance-contingent reward. Results showed that the inhibitoryprocesses were modulated by reward, with n-2 repetition costs incremented after reward delivery.Data suggest that reward-triggered reduction or elimination of switch costs may reflect enhancinginhibitory processes which are motivated by reward signals and targeted at the irrelevant task set. Thesefindings shed new light on the role of reward in cognitive control.

Keywords: Backward inhibition; Cognitive control; Interference; Reward; Task switching.

In daily life, people often encounter several tasksand are required to switch frequently among them.The ability to switch between tasks is an importantaspect of cognitive control. Many researchers areinterested in how human behaviour is adaptive ina multiple task environment by means of the task-switching paradigm (for reviews, see Kiesel et al.,2010; Monsell, 2003; Vandierendonck, Liefooghe, &Verbruggen, 2010). It is often found that switchingto another task is associated with longer reactiontimes (RTs) and/or higher error rates comparedwith repeating the same task. This switch cost mayreflect interference between different task sets(Allport, Styles, & Hsieh, 1994; Mayr & Keele,2000; Wylie & Allport, 2000). That is, whenperforming the current task, the irrelevant taskset interferes with the relevant task set and needsto be inhibited. This inhibition lingers for sometime and, when the previously inhibited taskbecomes relevant again, the switch cost emerges.

Contributions of between-task inhibition onswitch cost were studied by requiring participantsto switch among three tasks: A, B and C. Whenperforming a task (e.g., task A), it can be the sametask as that performed two trials earlier (i.e., thetask sequence is ABA) or it can be different (i.e.,the task sequence is CBA). The role of inhibition intask switching is demonstrated by comparing per-formance differences between these two condi-tions. It is reported that returning to a recentlyperformed task after one intermediate trial (i.e.,ABA) is more time-consuming and/or error pronerelative to a less recently performed task (i.e.,CBA), resulting in n-2 repetition costs (also calledbackward inhibition or lag-2 repetition costs; e.g.,Arbuthnott, 2008; Gade & Koch, 2007; Mayr &Keele, 2000). This effect is typically explained byassuming that the residual inhibition applied to theirrelevant task A is stronger when it was switchedaway more recently, which impairs switching backto this task when it becomes relevant again. Up till

Correspondence should be addressed to Baihua Xu, Department of Psychology and Behavioural Sciences, Xixi Campus,Zhejiang University, Hangzhou, Zhejiang Province, China. E-mail: huban@zju.edu.cn

The authors would like to thank Mei-Ching Lien, Iring Koch and two anonymous reviewers for their helpful comments on anearlier draft of this paper.

© 2014 Taylor & Francis

Journal of Cognitive Psychology, 2014Vol. 26, No. 2, 178–186, http://dx.doi.org/10.1080/20445911.2013.878717

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now, n-2 repetition cost has been taken as the mostconvincing evidence for inhibitory processes in taskswitching (Koch, Gade, Schuch, & Philipp, 2010).

Generally, switch costs are robust, and almostnever disappear. Even if the time interval betweentwo successive tasks is much lengthened to reducebetween-task interference as much as possible,switch costs still remain (Allport et al., 1994;Meiran, Chorev, & Sapir, 2000). These stubbornswitch costs are called residual switch costs. How-ever, some recent studies found reduced or elimi-nated switch costs when monetary reward wasrandomly provided or associated with one of thetasks (Kleinsorge & Rinkenauer, 2012; Savine,Beck, Edwards, Chiew, & Braver, 2010), indicat-ing that reward can compensate for performancedecrement in task switching. These findings areconsistent with the well-known facilitating effects ofreward on overt actions and diverse cognitive pro-cesses (e.g., Bijleveld, Custers, &Aarts, 2012; Braem,Verguts, Roggeman, & Notebaert, 2012; Della Lib-era & Chelazzi, 2006; Veling & Aarts, 2010).

However, it is unclear why reward can reduceswitch costs. Specifically, it remains a question howreward would affect inhibitory processes underly-ing task switching, given the fact that reward hasbeen demonstrated recently to exhibit not onlyenhancing but also disrupting effects on behaviourwhen conflict information exists. For instance,using the flanker task, van Steenbergen, Band,and Hommel (2009) found that reward counteractsconflict-adaptation effects, thus disrupting adjust-ments in cognitive control. In another study, Krebs,Boehler, and Woldorff (2010) adopted the Strooptask and observed that, although reward attenuatesperformance decrements induced by incongruentinformation in colour and word dimensions, it alsoimpedes performance when the reward-relatedinformation appeared in task-irrelevant worddimension. As a consequence, these studies raisethe intriguing question of whether reward wouldmagnify or diminish between-task inhibition.

In summary, we conducted the present studyfor the following three reasons: (1) inhibition playsan important role in generating switch costs, (2)reward can attenuate switch costs, but how itwould affect inhibitory processes remains un-known and (3) past research shows that rewardhas beneficial or disrupting effect on cognitiveprocesses. So, in the present study, we investigatedthe influence of reward on inhibitory processes intask switching. Specifically, we explored howreward would affect n-2 repetition costs. If rewardcan enhance inhibition to the irrelevant task, we

would expect to find larger n-2 repetition costsafter a reward trial, otherwise the size of n-2repetition costs would not change.

METHOD

Participants

Twenty students (mean age ± SD: 20.25 ± 1.21,12 female) took part in the experiment and werepaid ¥25 plus an average bonus of ¥2.95. All ofthem had normal or corrected-to-normal vision,and all were right-handed. They were naïve as tothe purpose of the study. Due to a programmingerror, part of the data from one participant waslost, so the final analyses included the remaining19 participants.

Materials and apparatus

Stimuli were shown on a standard cathode ray tube(CRT) monitor. All stimuli and feedback wordswere drawn in white and were presented against alight grey background. Each test display consistedof three characters: a capitalised letter (A, E, I, U,Q, T, B, D), a number (2–9) and a symbol (+ = </:;?!). Each character was about 0.8° high and 0.2°–0.5° wide with a viewing distance of 57 cm. In eachtrial, these three characters were all presented,appearing vertically in a column, and their relativepositions were randomly assigned. The verticaldistance between neighbouring characters was1.2° (centre to centre). These three characterswere surrounded by a circle, a diamond or ahexagon (all about 4.5° × 4.5°), serving as a taskcue to indicate which task to perform. The circlealways denoted the letter task, the diamond thenumber task and the hexagon the symbol task.Task cues were surrounded by reward cues. Theywere composed of four “¥” symbols or four smallsquares (0.5° × 0.5°), indicating reward trials or no-reward trials, respectively (see Figure 1).

Procedure

Participants were tested individually in a quiet,dimly lit room. Instructions were shown on thescreen and explained by an experimenter. Partici-pants were required to place the index and middlefingers of their right hands on the J and K keys ofthe computer keyboard. After 30 trials for prac-tice, participants engaged in two experimental

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phases: a baseline phase and a reward phase.Three tasks were intermixed within block. Forthe letter task, participants were required to judgewhether the letter was a vowel or a consonant. Forthe number task, they were asked to determinewhether the number was odd or even. For thesymbol task, they were required to decide whetherthe symbol was a mathematical or a text symbol.Although some symbols may belong to eithercategory, each symbol has its most typical andfamiliar use. Each symbol’s typical category waspreassigned, and participants were informed aboutthe assignment. Tasks were randomly assigned inevery trial with the constraint that task repetitionwas not allowed, so each trial could be eitherABA (i.e., the current task was the same as thatperformed two trials earlier) or CBA (i.e., thecurrent task was different from that performedtwo trials earlier). The baseline phase was used toset reward criteria for the following reward phase,and it consisted of four blocks of 61 trials each. Atrial started with a fixation, after which the taskcue and the reward cue were presented togethersimultaneously. The stimuli joined 600 ms later,with the task cue and the reward cue still appear-ing on the screen. Participants were instructed torespond as quickly and accurately as possible bypressing the J or K key with their right-hand indexand middle fingers. There were eight differentcategory-response mappings, labelled 1 to 8. Uponarriving, each participant was assigned one map-ping in sequence. After responses, all stimuli weredisplaced with the words “next trial” in the centreof the screen lasting for 500 ms. The next trialbegan 500 ms later.

After the baseline phase, participants wereasked to take a short break, and then the rewardphase began. During the reward phase, partici-pants were informed that they would earn addi-tional bonuses based on their performance on

some reward trials. Reward trials were denotedby four “¥” symbols surrounding the task cue,whereas no-reward trials were denoted by foursmall squares. It is worthwhile noting that thesetwo types of symbols were also presented in thebaseline phase, but participants were told thatthese symbols were irrelevant to the task, and theywere not aware that the reward phase wouldfollow. Reward trials occurred randomly with theconstraint that a succession of two reward trialswas not allowed. This is because our major interestwas the influence of reward on the following no-reward trial. As a consequence, we tried to includeas many no-reward trials as possible, and excludeall reward-reward sequences which were not use-ful for the present study. With this constraint,about one-third of all trials during this phase werereward trials, and the remaining two-thirds wereno-reward trials. For each participant, the medianRT on correct trials in the baseline phase was setas the reward criterion for each task. The proced-ure during this phase was basically identical to thebaseline phase, with the exception that partici-pants received different feedback, depending ontheir performance and trial type. Once participantsresponded correctly and faster than their criteriain a reward trial, a message “points + 10” wasshown after key presses for 500 ms. The morepoints participants gained, the more they would bepaid. In all other situations (including correct butslower responses and incorrect responses in re-ward trials, and all no-reward trials), responseswere followed by the words “next trial” for 500 msas feedback. The next trial began 500 ms later.The response–cue interval was the same across allconditions. In addition, the RT deadline was set to2500 ms, with slower RTs resulting in a message“too slowly”. The reward phase consisted of fourblocks of 92 trials each.

RESULTS

Trials following errors and the first two trials ofeach block were removed. For RT analyses, errorswere also excluded. From the remaining trials,RTs falling outside 3SDs were discarded (2.95%and 2.38% of all trials for the baseline phase andthe reward phase, respectively). The averagedRTs and error rates were submitted to repeated-measures analyses of variance (ANOVAs). Themean error rates and the SD were shown inTable 1.

Figure 1. Two examples of the stimulus display. Task cueswere represented by the shape surrounding the characters.Reward cues were denoted by four small signs (squares or ¥) inthe four corners.

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Baseline phase

This phase was mainly used for generating rewardcriteria in the reward phase. We found robust n-2repetition cost. RTs for ABA were 45 ms slowerthan for CBA, F(1, 18) = 18.812, p < .001, η2 =.511. Error rates also showed backward inhibition:Responses for ABA were less accurate than forCBA, F(1, 18) = 5.797, p < .05, η2 = .244.Furthermore, we ran an ANOVA to test whetherthe reward signs and squares made any differencein influencing participants’ performance. Eachtrial was sorted according to the type of cues:reward signs or squares. A 2 × 2 ANOVA withfactors of Transition (ABA vs. CBA) and CueType (reward sign vs. square) was conducted. Ascan be seen in Figure 2a, only the main effect ofTransition was significant, F(1, 18) = 17.362, p <.01, η2 = .491. The main effects of Cue Type andthe interaction were not significant, F(1, 18) =

2.940, p = .10; F(1, 18) = .001, ns. The resultsindicate that these two types of cues (reward signsor squares) have no different impact on theperformance when participants were not aware ofthe meaning of the signs.

Reward phase

In this phase, about one-third of all trials werereward trials. Participants actually received rewardon 74.49% of these reward trials. In addition, ageneral practice effect was found. A three-wayANOVA was conducted with Phase (baseline vs.reward phase), Reward (in the current trial, no-reward vs. reward) and Transition (ABA vs.CBA) as factors. Not surprisingly, the main effectswere significant for Phase, F(1, 18) = 116.701,p < .001, η2 = .866; for Reward, F(1, 18) = 15.236,p < .001, η2 = .458 and for Transition, F(1, 18) =37.284, p < .001, η2 = .674. Importantly, Phase andReward interacted significantly, F(1, 18) = 13.663,p < .01, η2 = .432. Other two-way interactions andthe three-way interaction were not significant, allFs < 1. Comparing Figure 2a and b, it has alreadybeen shown that the difference between the twolines in Figure 2a was not significant in the lastparagraph. Here, we found a significant differencebetween reward and no-reward trials in Figure 2b,F(1, 18) = 16.541, p < .001, η2 = .479. This

TABLE 1Mean error rates and SD (%) for each transition condition in

each phase

ABA CBA

Baseline phase 5.38 (3.47) 4.54 (2.96)Reward phase 7.68 (4.15) 6.74 (4.11)

Figure 2. Response times (RTs) as a function of task transition and type of reward cues in the (a) baseline phase and (b) rewardphase. Error bars represent the standard error of the mean.

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difference reflects the performance improvementattributable to reward incentives. Furthermore,the practice effect could be indicated by thesignificant difference between performance in thebaseline phase and no-reward trials in the rewardphase, F(1, 18) = 53.720, p < .001, η2 = .749. Thefact that Transition did not interact with bothPhase and Reward suggests that the inhibitionalready applied to a task would not be influencedby practice or reward. Practice and reward couldboth accelerate response times, but it seems thatthey have nearly equal impact on ABA and CBAsequences. As a result, n-2 repetition costsremained nearly the same in the two phases, nomatter whether reward was provided in thecurrent trial.

Though reward had no impact on the inhibitionalready applied to the current task, could theinhibition triggered to the irrelevant task beaffected by reward? For example, consider a tasksequence ABA (assuming the last A is rewarded).When performing task B, the preceding task Awould be inhibited. After that, the rewarded taskA—which is still in an inhibited state—needs to beperformed. Earlier analyses show that rewardwould not help task A recover from being inhib-ited (i.e., whether task A was rewarded would notinfluence n-2 repetition costs). Nonetheless, whenperforming the last task A, inhibition would be

triggered to the preceding irrelevant task B. Moreimportantly, since the last task A is a reward task,it may enhance the inhibition targeted at task B,compared to when task A is not rewarded. Toexplore the effects of reward on the inhibitiontriggered to the irrelevant task, we conducted anANOVA with RewardN-1 (reward in trial N-1, no-reward vs. reward) and Transition (ABA vs.CBA) as factors. The main effects were significant,both for RewardN-1, F(1, 18) = 16.778, p < .001,η2 = .482 and for Transition, F(1, 18) = 23.618, p <.001, η2 = .567. More importantly, their interactionwas also significant, F(1, 18) = 9.702, p < .01, η2 =.350. As shown in Figure 3a, the n-2 repetition costwas larger when trial N-1 was rewarded (74 ms),compared to when trial N-1 was not rewarded (20ms). Error rates revealed no significant effects.

The results thus far have clearly shown thatreward can increase the inhibition to the irrelevanttask, causing greater n-2 repetition costs. How-ever, before reaching this conclusion, anotherissue needs to be clarified. It may be noted thatthe reward manipulation in every trial was notindependent of each other (recall that two suc-cessive reward trials were not allowed), so weshould consider the situation in trial N-2. Morespecifically, when trial N-1 was a reward trial, trialN-2 could only be a no-reward trial; when trial N-1was a no-reward trial, trial N-2 could be either a

Figure 3. Response times (RTs) in the reward phase: (a) RTs as a function of task transition and reward in trial N-1, and (b) RTsas a function of task transition and reward in trial N-2. Error bars represent the standard error of the mean.

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reward or a no-reward trial. To explore thepossible influence of reward in trial N-2 onbackward inhibition, a three-way ANOVA wasperformed with RewardN-2 (reward in trial N-2),RewardN (reward in trial N) and Transition asfactors. The main effects were significant, both forRewardN, F(1, 18) = 14.288, p < .001, η2 = .443 andfor Transition, F(1, 18) = 7.822, p < .02, η2 = .303.RewardN-2 had no reliable main effect, F(1, 18) =2.220, p = .154, but it interacted reliably withTransition, F(1, 18) = 10.143, p < .01, η2 = .360, andit also had a marginally significant interaction withRewardN, F(1, 18) = 4.056, p = .059, η2 = .184. Theinteraction between RewardN and Transition andthe three-way interaction were not significant, allFs < .10. Since RewardN-2 interacted with Trans-ition and the three-way interaction was not signi-ficant, we collapsed data from no-reward andreward trials in trial N. As can be seen in Figure3b, when trial N-2 was a no-reward trial, the n-2repetition cost (49 ms) was reliable, t(18) = 4.740,p < .001, whereas when trial N-2 was rewarded,the n-2 repetition cost (−1 ms) was negligible,t(18) = .088, ns. The results suggest that rewardavailability in trial N-2 could affect the inhibitionapplied to the task in trial N-2. When reward isavailable in trial N-2, the task would be in a moreactivated state and thus difficult to be inhibited,especially in the current experimental settingswhere a no-reward trial would always follow areward one. A no-reward trial would furtherdemotivate participants to generate inhibition toa hard-to-inhibit task. Consequently, the n-2 repe-tition cost would be much smaller, even disappear.

DISCUSSION

The present study demonstrates the effect ofreward on inhibitory processes in task switching.The primary finding is that monetary incentivescan enhance inhibition triggered by between-taskinterference, causing greater n-2 repetition costs.Many cognitive processes can be explained in termsof inhibitory control, such as negative priming andinhibition of return. However, some researchershave argued that these well-known cognitive phe-nomena could also be interpreted by non-inhibitorymechanisms (MacLeod, Dodd, Sheard, Wilson, &Bibi, 2003; Neill, 2007; Tipper, 2001). Thesearguments lead us to consider the situation intask switching. Although some non-inhibitoryalternatives have been suggested in task switching,such as memory retrieval and stimulus–response

binding (Mayr & Kliegl, 2000; Wylie & Allport,2000), they cannot rule out the inhibitory mech-anism. In fact, n-2 repetition cost is the mostconvincing indicator of inhibition in task switch-ing (Koch et al., 2010). The inhibitory processescould be targeted at different levels and compo-nents. First, during the cue–stimulus interval,the irrelevant task set, as a whole, would beinhibited. Second, upon the appearance of thestimuli, the inhibitory processes could excludeirrelevant stimulus features or dimensions. Third,the inhibitory processes could be targeted atirrelevant but competing S–R mappings duringthe response selection/execution phase. Rewardcould strengthen all these inhibitory processes. Insum, the present findings suggest that the inhibi-tion applied to the irrelevant task is increased aftera reward signal, making participants concentratemore on the relevant task.

In addition to the primary finding that rewardcan enhance inhibition to an irrelevant task, wefurther showed two other issues concerning therelationship between reward and inhibition. First,reward has no influence on the inhibition alreadyapplied to a task. This was shown by the nullinteraction between Reward in trial N and Trans-ition. It seems that the inhibition could only decaypassively over time, but could hardly be modu-lated actively, even in a motivated situation. Thisis consistent with previous findings that n-2 repe-tition costs would decrease with longer response–cue interval, but not with longer cue–stimulusinterval. Second, once a task has been rewarded,it becomes harder to be inhibited, in particularwhen a no-reward task is followed. This wasreflected in the null inhibition effect when trialN-2 was rewarded. A reward task could makeanother irrelevant task in a more inhibited state.Meanwhile, the reward task would be more diffi-cult to be inhibited by another no-reward task.Also, the no-reward task following a rewardedtask could demotivate the inhibitory processes,which is consistent with the observation that manybehavioural effects disappeared after no-rewardtrials (e.g., Braem et al., 2012; Hickey, Chelazzi, &Theeuwes, 2010, 2011).

It seems that the enhanced n-2 repetition costsafter reward trials may reflect the effect of bothreward expectancy and reward feedback. On theone hand, the inhibitory processes should takeplace once the reward cues are encountered, andthis reward expectancy would affect the followingbehaviour. If, suppose, participants did not inhibitthe irrelevant task set when the reward cue was

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presented, they would not have shown a muchbetter performance during the reward phase.Furthermore, participants may be aware implicitlythat a no-reward trial would always follow areward trial, so inhibiting the irrelevant task inthe reward trial would do no harm to the nexttrial. On the other hand, although reward expect-ancy could induce to trigger more inhibitioncompared to no-reward trials, reward feedbackmay consolidate the effect of inhibition triggeredduring the earlier phase of a trial and make theeffect even larger. Thus, the enhancement ofinhibition was due to both reward expectancyand feedback. The present study does not aim atexploring the relative amount of contribution ofreward expectancy and feedback. This is also thereason why we included both kinds of trials onwhich participants actually did and did not receivereward into the analyses. At this time, we admitthat both factors contribute to the effect. In fact,many studies demonstrate the influence of rewardexpectancy or feedback on the cognitive processes(Braem et al., 2012; Hickey et al., 2010, 2011; vanSteenbergen et al., 2009). We think it is a goodissue to explore how reward expectancy andfeedback would affect inhibitory processes in thefuture.

Earlier results exhibit opposite effects of re-ward on interference-induced cognitive adjust-ments. For example, van Steenbergen et al.(2009) observed that the reduced congruencyeffect usually found after incongruent trials in aflanker task became equal to the congruencyeffect after congruent trials when reward wasdelivered after response to the incongruent trial,showing a failure to cognitive adjustments. How-ever, Braem et al. (2012) found opposite resultswith the same paradigm, demonstrating a signific-ant conflict–adaptation effect when reward wasintroduced. These contradictory results made usfeel uncertain about, therefore necessary to exam-ine, whether monetary incentives delivered into atask switch paradigm would cause smaller orgreater inhibition to the irrelevant task set. Ascan be seen clearly in our experiment reportedhere, inhibitory processes underlying task switch-ing can be modulated by monetary incentives, withgreater inhibition being exerted when reward isprovided, and we take this as an indicator ofsuccessful cognitive adjustments.

Reward is conceptualised to have multiplepsychological components: affective, motivationaland learning (Berridge & Robinson, 2003). Webelieve that our results reveal the motivational

aspect of reward. Within our experimental con-text, participants’ exertion of more inhibition tothe irrelevant task in reward trials could maximisetheir gains, so the reward cue had motivationaleffect on participants. Alternatively, van Steenber-gen et al.’s (2009) reward was not based onparticipants’ accuracy, and their reward was sig-nalled randomly after participants’ responses, sotheir reward manipulation might reflect the affect-ive effect of reward. In fact, they used smiley facesas reward feedback, which were inherently affect-ive. On the other hand, our study is in line withBraem et al. (2012), who also used value incre-ments (e.g., +10) as reward feedback and showedthe motivational effect of reward. However, ourresults extend their associative account of reward(Braem et al., 2012; Verguts & Notebaert, 2009)by showing the effect of reward on cognitivecontrol via inhibition, not mere association orbinding.

We speculate that the reward-induced perform-ance depends on midbrain dopaminergic neuronsand their projections to the nucleus accumbens, anarea usually linked to motivation, thereby furtherconnecting to frontal regions, including theanterior cingulate cortex and right inferior frontalgyrus, which play an important role in conflictdetection (Botvinick, Cohen, & Carter, 2004) andinhibitory processing (Aron, Robbins, & Poldrack,2004), respectively. In this way, the dopaminesystems together with the motivational-cognitivecircuits in the brain enhance the inhibitory pro-cesses in task switching. Furthermore, we assumethat the neuronal activities would be greatestduring the response selection/execution phase,since conflict during this phase has been demon-strated as the most probable trigger of task-setinhibition (Philipp, Jolicoeur, Falkenstein, &Koch, 2007; Schuch & Koch, 2003). In future,neuroimaging and event-related potentials (ERP)studies are highly desirable to further explorethese relating issues.

The few papers addressing the relationshipbetween reward and task switching all demon-strated reduced or disappeared switch costs inreward conditions (Kleinsorge & Rinkenauer,2012; Savine et al., 2010). Our research takes afurther step to examine the reason of the reduc-tion or elimination of switch costs, and sheds newlight on the role of reward in shaping task-switch-ing performance. The sources of switch costs havebeen attributed mainly to the time taken toreconfigure a new task set or resolve between-task interference. Accordingly, reward-induced

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reduction of switch costs discovered by earlierstudies indicates that reward may facilitate recon-figuration of the new task set or increase inhibitionof the irrelevant task set. Our results support thelatter explanation. However, we do not mean thatreward has no effect in reconfiguration processes,but further experiments are needed to specificallyexamine the role of reward in reconfiguration pro-cesses. Our results clearly show that reward cannot only affect inhibitory processes but alsoincrease inhibition to the irrelevant task set.

Over the last few decades, there has been awealth of studies investigating how emotional, moti-vational or personality factors influence perceptual,attentional, memory or cognitive control processes.These factors have been underestimated before,and new empirical findings are accumulating rapidly.Our study fills the gap between motivation-inducedperformance enhancement and inhibitory mechan-isms in task switching. Future work may includeinvestigation of clinical samples, such as peoplewith depression or Parkinson’s disease. The dis-order of the nervous system may render thesepeople insensitive to reward information, and thisin turn may have different impact on the inhibitoryprocesses compared to normal people. The invest-igation of clinical people, as a supplement, couldprovide additional evidence from a different pointof view. Also, it is helpful for the exploration of theneurobiological basis underlying mechanisms ofreward-modulated inhibition.

Original manuscript received June 2013Revised manuscript received November 2013Revised manuscript accepted December 2013

First published online January 2014

REFERENCES

Allport, A., Styles, E. A., & Hsieh, S. (1994). Shiftingattentional set: Exploring the dynamic control oftasks. In C. Umilta & M. Moscovitch (Eds.), Attentionand performance XV: Conscious and nonconsciousinformation processing (pp. 421–452). Cambridge,MA: MIT Press.

Arbuthnott, K. (2008). The effect of task location andtask type on backward inhibition. Memory & Cogni-tion, 36, 534–543. doi:10.3758/MC.36.3.534

Aron, A. R., Robbins, T. W., & Poldrack, R. A. (2004).Inhibition and the right inferior frontal cortex.Trends in Cognitive Sciences, 8, 170–177. doi:10.1016/j.tics.2004.02.010

Berridge, K. C., & Robinson, T. E. (2003). Parsingreward. Trends in Neurosciences, 26, 507–513. doi:10.1016/S0166-2236(03)00233-9

Bijleveld, E., Custers, R., & Aarts, H. (2012). Adaptivereward pursuit: How effort requirements affect un-conscious reward responses and conscious rewarddecisions. Journal of Experimental Psychology: Gen-eral, 141, 728–742. doi:10.1037/a0027615

Botvinick, M. M., Cohen, J. D., & Carter, C. S. (2004).Conflict monitoring and anterior cingulate cortex:An update. Trends in Cognitive Sciences, 8, 539–546.doi:10.1016/j.tics.2004.10.003

Braem, S., Verguts, T., Roggeman, C., & Notebaert, W.(2012). Reward modulates adaptations to conflict.Cognition, 125, 324–332. doi:10.1016/j.cognition.2012.07.015

Della Libera, C., & Chelazzi, L. (2006). Visual selectiveattention and the effects of monetary rewards. Psy-chological Science, 17, 222–227. doi:10.1111/j.1467-9280.2006.01689.x

Gade, M., & Koch, I. (2007). The influence of overlap-ping response sets on task inhibition. Memory &Cognition, 35, 603–609. doi:10.3758/BF03193298

Hickey, C., Chelazzi, L., & Theeuwes, J. (2010). Rewardchanges salience in human vision via the anteriorcingulate. Journal of Neuroscience, 30, 11096–11103.doi:10.1523/JNEUROSCI.1026-10.2010

Hickey, C., Chelazzi, L., & Theeuwes, J. (2011). Rewardhas a residual impact on target selection in visualsearch, but not on the suppression of distractors.Visual Cognition, 19(1), 117–128. doi:10.1080/13506285.2010.503946

Kiesel, A., Steinhauser, M., Wendt, M., Falkenstein, M.,Jost, K., Philipp, A. M., & Koch, I. (2010). Controland interference in task switching: A review. Psy-chological Bulletin, 136, 849–874. doi:10.1037/a0019842

Kleinsorge, T., & Rinkenauer, G. (2012). Effects of mon-etary incentives on task switching. Experimental Psy-chology, 59, 216–226. doi:10.1027/1618-3169/a000146

Koch, I., Gade, M., Schuch, S., & Philipp, A. M. (2010).The role of inhibition in task switching: A review.Psychonomic Bulletin & Review, 17(1), 1–14. doi:10.3758/PBR.17.1.1

Krebs, R. M., Boehler, C. N., & Woldorff, M. G. (2010).The influence of reward associations on conflictprocessing in the Stroop task. Cognition, 117, 341–347. doi:10.1016/j.cognition.2010.08.018

MacLeod, C. M., Dodd, M. D., Sheard, E. D., Wilson,D. E., & Bibi, U. (2003). In opposition to inhibition.In B. H. Ross (Ed.), The psychology of learning andmotivation (Vol. 43, pp. 163–214). San Diego, CA:Academic Press.

Mayr, U., & Keele, S. W. (2000). Changing internalconstraints on action: The role of backward inhibi-tion. Journal of Experimental Psychology: General,129(1), 4–26. doi:10.1037/0096-3445.129.1.4

Mayr, U., & Kliegl, R. (2000). Task-set switching andlong-term memory retrieval. Journal of ExperimentalPsychology: Learning, Memory, and Cognition, 26,1124–1140. doi:10.1037/0278-7393.26.5.1124

Meiran, N., Chorev, Z., & Sapir, A. (2000). Componentprocesses in task switching. Cognitive Psychology, 41,211–253. doi:10.1006/cogp.2000.0736

Monsell, S. (2003). Task switch. Trends in CognitiveSciences, 7, 134–140. doi:10.1016/S1364-6613(03)00028-7

REWARD ENHANCES BACKWARD INHIBITION 185

Dow

nloa

ded

by [

McM

aste

r U

nive

rsity

] at

10:

04 2

8 N

ovem

ber

2014

Neill, W. T. (2007). Mechanisms of transfer-inappropriateprocessing. In D. S. Gorfein & C. M. MacLeod (Eds.),Inhibition in cognition (pp. 63–78). Washington, DC:American Psychological Association.

Philipp, A. M., Jolicoeur, P., Falkenstein, M., & Koch, I.(2007). Response selection and response execution intask switching: Evidence from a go-signal paradigm.Journal of Experimental Psychology: Learning, Mem-ory, and Cognition, 33, 1062–1075. doi:10.1037/0278-7393.33.6.1062

Savine, A. C., Beck, S. M., Edwards, B. G., Chiew, K. S.,& Braver, T. S. (2010). Enhancement of cognitivecontrol by approach and avoidance motivationalstates. Cognition and Emotion, 24, 338–356. doi:10.1080/02699930903381564

Schuch, S., & Koch, I. (2003). The role of responseselection for inhibition of task sets in task shifting.Journal of Experimental Psychology: Human Percep-tion and Performance, 29(1), 92–105. doi:10.1037/0096-1523.29.1.92

Tipper, S. P. (2001). Does negative priming re-flect inhibitory mechanisms? A review and in-tegration of conflicting views. The Quarterly Journal

of Experimental Psychology: Section A, 54, 321–343.doi:10.1080/02724980042000183

Vandierendonck, A., Liefooghe, B., & Verbruggen, F.(2010). Task switching: Interplay of reconfigurationand interference control. Psychological Bulletin, 136,601–626. doi:10.1037/a0019791

van Steenbergen, H., Band, G. P. H., & Hommel, B.(2009). Reward counteracts conflict adaptation:Evidence for a role of affect in executive control.Psychological Science, 20, 1473–1477. doi:10.1111/j.1467-9280.2009.02470.x

Veling, H., & Aarts, H. (2010). Cueing task goals andearning money: Relatively high monetary rewardsreduce failures to act on goals in a Stroop task.Motivation and Emotion, 34, 184–190. doi:10.1007/s11031-010-9160-2

Verguts, T., & Notebaert, W. (2009). Adaptation bybinding: A learning account of cognitive control.Trends in Cognitive Sciences, 13, 252–257. doi:10.1016/j.tics.2009.02.007

Wylie, G., & Allport, A. (2000). Task switching andthe measurement of ‘switch costs’. PsychologicalResearch, 63, 212–233. doi:10.1007/s004269900003

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